This invention relates to ensuring uniform contact in electrical connector, and in particular to a resilient pressure pad providing uniform contact pressure for multiple electrical contacts.
Flexible conductor strips, commonly referred to as xe2x80x9cflex strips,xe2x80x9d are often used to electrically interconnect electrical devices such as circuit boards in an assembly, connectors on a circuit board, and other electrical devices that may experience relative motion. Flex strips are generally well-known in the art as multiple flat electrical conductors usually laid out in parallel strips and encased in a flexible nonconductive material. The resulting flexible electrical interface, i.e., the flex strip, can be bent and twisted within limits. Often, electrical connection means are provided at either end of the conductive strip by either pins or holes for insertion of male pins. In such instances, electrical interconnection is commonly provided by solder joints. Electrical contact can be made by other means as well. For example, button contacts formed at the ends of the individual constructive strips can be held in contact with mating contact pads on the electrical device. In practice, this latter type of electrical contact is not unlike an over center switch wherein one contact is stationary or fixed and the other contact is pressed against the stationary contact with a spring force. Generally such switches are limited to a single pair of mating contacts in part because of a need to apply uniform contact pressure to each of the pairs of mating electrical contacts. Uniform contact pressure is difficult to ensure when a single spring is used to uniformly load more than one contact pair. The difficulty of supplying uniform pressure is greatly increased when the number of electrical contact pairs is increased. Greatly increasing the number of contacts, reducing the contact pad size, and decreasing the current passed through the contact interface are all factors that exacerbate the already difficult problem.
Generally, the prior art solutions provide a non-uniform loading across an array of rows and columns of contact pad pairs that either fails to provide reliable contact pressure to some of the contact pads, or load some of the contact pads so severely that they are crushed. Therefore, a mechanism providing truly uniform loading across an array of contact pad is desirable.
The present invention provides a clamp for coupling electrical contacts on a flexible conductor strip, or flex strip, with a substantially uniform pressure against mating contacts on another device, such as a circuit board. The clamp includes a housing formed with a recess of substantially uniform depth. A thin pad of elastomeric insulation material is sized to fit snugly within the width and breadth of the housing. The elastomeric pad is formed with a substantially uniform thickness greater than the depth of the recess in the housing and thus extends beyond the recess depth. An array of substantially uniform pressure areas are formed in the pad surface at interstices between an array of evenly spaced rows and columns of cavities formed in the pad thickness. Clamping means, for example, one or more threaded fasteners, secures the housing to a mating surface, such as a circuit board.
According to one aspect of the invention, a rigid metal backing plate is provided opposite the recess in the housing to strengthen the housing. Preferably, the clamping means also secures the backing plate to the mating surface.
According to one aspect of the invention, the resilient pad thickness is approximately double that of the depth of the recess in the housing.
According to another aspect of the invention, the cavities formed in the elastomeric pad are cylindrical cavities extending approximately halfway through the pad thickness.
According to other aspects of the invention, the present invention provides a various methods for clamping multiple rows and columns of electrical contacts with substantially uniform pressure.